Stabilization of Pickering emulsion with surface-modified titanium dioxide for enhanced photocatalytic degradation of Direct Red 80

Surface modification of titanium dioxide (TiO2) was carried out with salicylic acid (SA) to generate an efficient Pickering emulsion (PE)-based photocatalytic system. The PE was stabilized with 0.5 and 1.0 mg mL(-1) of TiO2 and SA-TiO2 by using cyclohexane and a synthetic aqueous Direct Red 80 (DR 80) solution (0.4:1) as the oil and water phases, respectively. The photocatalytic activity of solution-dispersed TiO2 was compared with that of the PE-based photocatalytic system for DR 80 degradation. In almost all PE-based photocatalytic systems, 100% color removal of DR 80 was observed within 15-60 min, compared to 76% and 100% color removal, achieved after 120 min, using 0.5 and 1.0 mg mL(-1) solution-dispersed TiO2, respectively. The estimated reaction rates of the PE-based photocatalytic system, as calculated using the Langmuir-Hinshelwood kinetics model, were almost double to those obtained for solution-dispersed TiO2. However, the addition of a free oil phase adversely affected the photocatalytic activity, and the lowest DR 80 degradation percentage was observed using 0.5 or 1.0 mg mL(-1) TiO2. The results demonstrated that a functional PE was successfully stabilized with SA-TiO2, and enhanced photocatalytic degradation of the azo dye was achieved in an effective and novel way. (C) 2016 Elsevier B.V. All rights reserved.